1. Field of the Invention
The present invention relates to a coupling structural body of optical parts, a method of manufacturing the same, and an optical switch module and, more particularly, a coupling structural body of optical parts such as an optical propagation system, an image forming system, and an optical deflecting system employed in an optical signal switching system (switching device, optical signal cross-connecting device) arranged at cross points of an optical network, a method of manufacturing the same, and an optical switch module.
The present invention relates to a two-dimensional lens array having a plurality of two-dimensional lenses each executes collimation or convergence of an optical signal propagated through a two-dimensional optical waveguide, an optical switch having this two-dimensional lens array, and a method of manufacturing the two-dimensional lens array.
2. Description of the Prior Art
The transmission band in the optical communication keeps on widening in recent years, and the higher speed and the larger capacity of the optical communication are advanced with the progress of the wavelength multiplexing technology. In order to establish the optical fiber network in the trunk communication network, the device for switching the destination of the optical signal is required.
The mainstream of such switching device was the optical cross-connecting device having an operation mode such that an optical signal is converted into an electric signal once, then the connection is switched in the state of the electric signal, and then the electric signal is converted into the optical signal once again. The electric switch such as a crossbar switch constructed by electronic switches, or the like was employed for switching in the state of the electric signal. However, when a data communication rate exceeds 10 Gb/s, it becomes difficult to switch the connection by using the electric switch.
If the optical switch that can switch directly the light propagation path is used in place of the electric switch to eliminate the photo-electric conversion, switching of the optical signal that does not depends on a rate (frequency) of the optical signal can be implemented. For this reason, there is a tendency such that the optical cross-connecting device using the optical switches is developed.
In the matrix-switch that employs the 2×2 switch as the base, an absolute value of loss and variation between ports become a problem if the number of ports is increased. Therefore, the analog optical deflection type switch, which has a small optical loss between paths, is preferable. More particularly, the switch of the optical beam switching type that employs the deflection by the micromirror can be used. There is the switch in which the micromirrors are integrated three dimensionally by using MEMS (microelectromechanical system) technology.
However, according to the optical switch in the MEMS technology, a size is large even in a 32×32 scale and a module size including the optical input/output port (fiber connector) becomes several tens cm square.
Meanwhile, if a plurality of m×n optical switches that are formed on a two-dimensional substrate are arranged to construct an optical switch group having a two-dimensional optical input/output port arrangement, a module size can be remarkably reduced into a small scale.
Therefore, a method of constructing the optical switch group on the two-dimensional substrate is promising for the optical cross-connecting switch.
The optical switch module constituting the optical switch group on the two-dimensional substrate is composed of optical parts such as a channel waveguide, a two-dimensional lens, an optical deflector element, etc. Each optical part is constructed by laminating an underlying cladding layer, a core layer, and an overlying cladding layer on a quartz substrate, and then patterning the core layer into a desired shape. The core layer constitutes a slab waveguide serving as a main optical waveguide, and causes a light to propagate in a flat plane.
In case the optical parts are to be arranged on the substrate, the light that is propagated through the optical waveguide must be optically coupled between the optical parts. Hence, the core layers of respective optical parts are opposed to each other in the coupling portion between the optical parts while an air layer is put therebetween.
However, in the coupling portion, which has the two-dimensional lens, out of the coupling portions between the optical parts, the light that is propagated through the optical waveguide must be collimated two-dimensionally and then coupled optically to the slab waveguide. In this case, there is the problem such that it is difficult to couple the light to the slab waveguide at a high efficiency.
This situation will be explained in detail. If the light is coupled optically by using the conventional two-dimensional lens, the air layer is interposed (in opposing portions) between the two-dimensional lens as the coupling portion and the slab waveguide. Thus, since the emitted light is converged in the in-plane direction but such light is diverged in the out-plane direction, a coupling efficiency is lowered. Also, a loss due to the reflection is increased by an increased difference in the refractive index between inside of the two-dimensional lens and outside thereof at the end surface thereof.
In order to overcome this problem, the prior application (Patent Application No. 2001-332169) filed by the same applicant as this application describes an example such that the resin of which the refractive index is larger than that of the atmosphere is buried in the opposing portion. According to this, first the filling resin film is formed by the patterning, and then a resin film to form the core layers is formed thereon, followed by polishing the resin film to form the core layers so as to planarize a surface thereof. It results in formation of the core layers putting the filling resin film therebetween. However, according to this forming method, the manufacturing steps become complicated and also control of a polished amount is needed.
The optical signal is suitable for the high-speed/large-capacity signal transmission. In the long-haul trunk communication system, the signal transmission using the optical signal has already been put into practical use. The optical switch for switching the transmission route of the optical signal is indispensable in such system. As the approach of implementing this optical switch, various systems have been proposed. In this case, for example, the optical switch using the optical deflector element is expected to bring the high-speed switching operation. Such optical deflector element is provided with the crystal, as the optical waveguide, having an electro-optical effect such that the refractive index is changed by the electric field. Prism-like electrodes are formed on and under the optical waveguide, and deflect the light that is propagated through the optical waveguide by the voltage applied to the electrodes.
FIGS. 1A and 1B are views showing an example of a configuration of a part of the optical switch using the optical deflector element in the prior art. FIG. 1A is a plan view showing a part of the optical switch, and FIG. 1B is a sectional view taken along a XI—XI line in FIG. 1A.
FIGS. 1A and 1B show, as an example, input-side constituent elements of an optical switch 800 having 8 input channels. The optical switch 800 on the input side is provided with an optical input waveguide portion 820, a collimator portion 830, and an optical deflector element portion 840. The optical switch 800 on the output side is provided with a common optical waveguide 850. In this optical switch 800, for example, the optical input waveguide portion 820, the collimator portion 830, and the common optical waveguide 850 are provided integrally on a common substrate 801, and then the optical deflector element portion 840 is mounted on this substrate 801.
A plurality of optical input waveguides 821, each corresponds to each input channel, are formed in the optical input waveguide portion 820. An optical fiber, or the like, for example, is connected to an incident end of each optical input waveguide 821. The optical signals are incident on the optical fibers respectively.
A plurality of collimator lenses 831, each corresponds to each optical input waveguide 821, are formed in the collimator portion 830. Each collimator lens 831 has a waveguide layer 832 as the slab optical waveguide on which the optical signal is incident from the optical input waveguide 821, and an air-gap filling layer 833 which is formed of the medium being different from the waveguide layer 832 in the refractive index. In the air-gap filling layer 833, an air-gap region that passes through the core layer and overlying/underlying cladding layers in the waveguide layer 832 is filled with a fluororesin, or the like to prevent the diffusion of light, for example. Then, an end surface of the waveguide layer 832 opposing to the air-gap filling layer 833 is shaped into a circular cylindrical surface, for example, to constitute a lens curved surface 834 of the two-dimensional lens. According to such structure, in each collimator lens 831, the optical signal that is propagated from the optical input waveguide 821 to spread radially in the waveguide layer 832 is converted in the parallel light by the lens curved surface 834, and then is emitted to the optical deflector element portion 840.
A plurality of optical deflector elements 841, each corresponds to the input channel, are provided in the optical deflector element portion 840. In each optical deflector element 841, the refractive index in a slab optical waveguide 842 is changed when the voltages is applied to the slab optical waveguide 842, which is made of the material having the electro-optical effect, via a prism-type electrode 843 serving as a lower electrode and a conductive substrate 844 serving as an upper electrode. Thus, the propagation direction of the incident optical signal is changed.
The common optical waveguide 850 is the slab optical waveguide which propagates commonly all optical signals, of which the connection is switched between the channels on the input and output sides. The common optical waveguide 850 transmits the optical signal that passes through the optical deflector element portion 840 to the output side.
In this case, the common optical waveguide 850 on the output side are provided with the constituent elements that are similar to the optical input waveguide portion 820, the collimator portion 830, and the optical deflector element portion 840, as shown in FIGS. 1A and 1B, in the opposite direction to the common optical waveguide 850. In other words, the common optical waveguide 850 on the output side is provided with output-side optical deflector element portion, light converging portion, and optical output waveguide portion. Those portions have the plural optical deflector elements, the plural light converging lenses, and the plural optical output waveguides to correspond to the number of output channels respectively. Then, the optical signal that propagates through the common optical waveguide 850 is incident on the corresponding light converging lens since its propagation direction is changed by the optical deflector element on the output side, and then such optical signal is focused onto the corresponding optical output waveguide by the light converging lens and then is output to the outside from the optical output waveguide.
According to such configuration, in the optical switch 800, the propagation direction of the input optical signal is changed in the common optical waveguide 850 by controlling the voltage applied to the optical deflector elements on the incident side and the emissive side in the common optical waveguide 850. Thus, the connection between any input channel and any output channel can be switched.
By the way, in the above optical switch 800, the light that propagates through the waveguide layer 832 from the optical input waveguide 821 is collimated by the lens curved surface 834 in the collimator portion 830. However, the light emitted from the optical input waveguide 821 propagates through the waveguide layer 832 to spread radially. Therefore, in the waveguide layer 832, most of the incident light propagates through the area in which the light can be collimated by the lens curved surface 834. However, actually a part of the light propagates to the outside of this area.
In this manner, the light outside this area which can collimate such light propagates to the neighborhood of the edge portion of the lens curved surface 834 or to the neighboring lens curved surface 834. Thus, there are some cases that the stray light is generated at these portions. For example, the light that is propagated to the edge portion of the lens curved surface 834 is caused to spread in respective directions at this portion, and then the light that is propagated to the neighboring lens curved surface 834 is emitted from the lens curved surface 834 in the direction that is different from the direction to direct.
In particular, in the case of the optical switch 800 having a plurality of input channels, the collimator portion 830 has a configuration such that the lens curves surfaces 234 of the two-dimensional lenses are aligned to correspond to respective input channels. Therefore, there was a serious problem such that the crosstalk is generated due to the light that propagated to the neighboring lens curved surface 834.
Also, in the light converging lens in the light converging portion that is provided to the common optical waveguide 850 on the output side, it is possible that a part of the light emitted from the optical deflector element on the preceding stage is not focussed onto the optical output waveguide on the output side. In this case, a part of the light is incident on the cladding area that surrounds the each optical output waveguide. In some cases, such light exerts a bad influence on the optical signal that propagates through the optical output waveguide.